Glass as stable as crystal: Homogeneity leads to stability

Date:
November 17, 2021
Source:
Institute of Industrial Science, The University of Tokyo
Summary:
Researchers have obtained new insights into the process of
crystallization in glasses that can lead to a loss of transparency
and mechanical strength. The researchers are the first to relate
the coordinated atomic dynamics that lead to "devitrification"
with a physical mechanism. This research may lead to improvements
in the long term stability of industrial glass.



FULL STORY ========================================================================== Researchers have obtained new insights into the process of crystallization
in glasses that can lead to a loss of transparency and mechanical
strength. The researchers are the first to relate the coordinated atomic dynamics that lead to "devitrification" with a physical mechanism. This research may lead to improvements in the long term stability of industrial glass.


========================================================================== Scientists from The University of Tokyo Institute of Industrial Science
used computer simulations to study the aging mechanism that can cause
an amorphous glassy material to turn into a crystal. They find that
removing tiny irregularities in local densities help prevent the atomic "avalanches" that trigger ordered structure formation. This work may
lead to more stable glassy materials, including for pharmaceutical applications.

Glasses are highly unusual solids in that they lack an organized crystal structure. In fact, they are more like "frozen liquids," because the
atoms can get stuck in non-equilibrium positions. Over time, some glasses experience an aging process or devitrification, in the latter of which
the amorphous configuration settles into a more regular structure. In
most cases, devitrification is undesirable, as it can turn previously transparent materials opaque. In addition to aesthetic considerations,
the lack of stability can cause damage to glass panes, as well as pharmaceuticals or optical media.

However, the physical mechanism that triggers aging or devitrification
remains poorly understood.

The team of researchers, led by The University of Tokyo Institute of
Industrial Science, used computer simulations to study the process of devitrification.

Instead of thermal annealing, the team took a novel approach by
starting with a "conventional glass" and progressively removing
inhomogeneities in density until a "uniform glass" was formed. This
new state showed unprecedented stability against devitrification. Lead
author Dr. Taiki Yanagishima says, "This uniform glass state shows
there is a clear connection between the stability of a glass state and
its mechanical homogeneity." As with other forms of crystal growth, devitrification starts when a tiny "seed" crystal, called a nucleus,
recruits neighboring atoms to arrange themselves in the same pattern. But unlike in liquids, the "seeds" in glasses only grow when they are given
a shake by large intermittent coordinated movements of atoms called "avalanches." In previous work, the researchers showed that these sudden
events corresponded to destabilizations of the load- bearing network
that spans the entire sample, and hypothesized that they were the only mechanism by which atoms may rearrange themselves. Making the glass more uniform prevents this relaxation and devitrification, even when nuclei are present. "When avalanches are prevented, nuclei that normally would grow
into crystals are instead frozen in their glassy state," senior author Professor Tanaka says. This leads to the possibility that by making the
number of load- bearing atomic neighbors more uniform across the sample, ultra-stable glasses may be formed. This "mechanical homogenization"
may open the way for stronger and more stable glasses.

========================================================================== Story Source: Materials provided by Institute_of_Industrial_Science,_The_University_of_Tokyo.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Taiki Yanagishima, John Russo, Roel P. A. Dullens, Hajime
Tanaka.

Towards Glasses with Permanent Stability. Physical Review Letters,
2021; 127 (21) DOI: 10.1103/PhysRevLett.127.215501 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211117095940.htm

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